The product called "dry silver" developed by Minnesota Mining and Manufacturing Co., U.S.A. is well known as the dry processing photographic material which overcame the drawbacks of silver halide wet processing while maintaining the photosensitivity, gradation and good image quality of silver halides.
Dry silver contains silver behenate which is a light-stable, colorless or white organic silver salt, and produces a silver image by the redox reaction when heated together with a reducing agent to 100.degree. C. or more. Silver behenate is one of the indispensable components of Dry silver.
The dry silver photographic material is generally prepared by coating on a support with the solution composed of a polymer dispersion of an organic silver salt in adding a silver halide forming agent, in which a part of the organic silver salt has been converted to a silver halide, a reducing agent (developing agent) and various additives. Alternatively, the dry silver photographic material may be prepared by coating on a support with the solution composed of a polymer dispersion of organic silver salt, a silver halide that has been separately prepared previously, a reducing agent (developing agent) and various additives. The above coating is followed by drying, to form a light-sensitive layer. In this material, an image can be formed using a thermal head, regardless of the presence or absence of the silver halide. That is, the dry silver recording material can also be used as a thermal recording material.
The image layers of such recording materials are advantageous in that the increased concentration of organic silver salts contained therein for obtaining high-density images allows the redox reaction to proceed at ordinary temperatures. In turn, this reduces shelf life. In order to enhance the shelf life, the use of antifoggants is known. However, the use of antifoggants in large amounts for obtaining a sufficient antifogging effect is problematic in that dynamic color development, one of indices of color development, is deteriorated. Furthermore, organic solvent coating solutions used to prepare the above-mentioned dry silver photographic materials present a problem that explosion-proof equipment is required.